Interference-neutralizing arrangement



Aug. 11, 1925. 1,548,862

g O. B. BLACKWELL INTEHFERENCE NEUTRALI ZING ARRANGEMENT .Filed Aug. 14,1920 f l@ /f l L Lib y g. /ac/we ATTORNEY Patented Aug. 1l, 1925.

UNITED STATES PA'rr-:trry OFFICE.

OTTO B. IBLACKWELL, F GARDEN CITY, NEW YORK, ASSIG-NOR'TO AMERICAN TELE-PHONE .AND TELEGRAPH COMPANY, A CORPORATION 0F NEW YORK..-

INTERFERENCE-NEUTRALIZING- ARRANGEMENT.

Application led August 14, 1920. Serial No. 403,549.

To all whom it may concer/:

Be it known that l, O'rro B. BLACKWELL, residing at Garden City, in thecounty of Nassau and State of New York, have inu vented certainImprovements in interference-Neutralizing Arrangements, of which thefollowing is a specification. l

rlhis invention relates to signaling systems and especially to means forneutralizing voltages that may be induced in electrical circuits bycauses extraneous to the circuits themselves, in order to prevent suchvoltages aecting the receiving apparatus associated with s uch circuits.

have been proposed for the neutralization of interfering voltages inlong signal-ing circuits, such as, for example, submarine cable.circuits which are adapted for duplex opera- 2'0 tio'n. A proposedarrangement provides means for equalizing the impedance to ground of thesignaling arm of the duplex network, and the sea ground connection ofthe said network by inserting at the sea ground an artificial line tobalance the submarine cable.. I'f the signaling conductor and theconductor constituting the sea ground connection remain balanced and areexposed to the'same interference, theywill both be raised to the samepotential and consequently there will be no diierence of potentialbetween them. Accordingly, the receiving apparatus connected across theduplex network will not be ailected lbythe eii'ect of the interferenceupon the conductors.

Experience shows, however, that it is dificult to maintain the balanceof a long circuit, such as a submarine cable circuit, and

4o consequently there may be a difference between the impedance toground of the signaling conductor and the conductor grounded through theartificial line. This will result in a dllerence of potentialfacross theduplex a5 network which affects the receiving apparatus associatedtherewith.

It is the object of this invention to' provide means whereby anydiierence of potential caused by some interferingv agency,

60 which may arise or exist by virtue of the imperfect balance betweenthe two sides of the said circuit, may be substantially reduced orneutralized.

This invention will be more clearly under- As is well known, variousarrangements In the arrangement of submarine cablev circuits, it is'customary to have the trans- Jmitting and receiving apparatus of theterminal circuits located in ofces which, as .a rule, are not locateddirectly at the shore yend of the submarine cable, but at some etldistance inland, and the said terminal circuits are usually connectedwith the submarine cables and the sea grounds by cable conductorsextendin between the oiiice and the shore. Thus, in ig. l., S1 and S2represent vtwo such terminal circuits. The circuit S, embraces the ratioarms 10 and 11, to the junction pointof which is connected atransmitting device 12 which may be of any well known type, as iorexample. a tape transmitter. winding 13 o the transformer T2 by means ofwhich received impulses are transmitted to the winding 14 and therebyimpressed across the input side ofthe receiving apparatus R1. The arm 10is connected by the conductor 23 to conductor 1 of the cable thatextends from the point A of terminal circuit to a point B where itjoinsI the submarine cable conductor: lThe distant end of the cable `.isconnected with a terminal circuit which may be either of the sametype asthat shown in Fig. 1 or of any of the welll' known types used intelegraphy. The point B represents the terminus of the submarine cableconductor and correspondsin position to the point D where the sea groundof the system is located. The arm 11 is connected through'the artificialnetworks 5 `and 7 of the terminal circuit to the conductor 2 of thecable that extends from the point C of the terminalcircuit to a point Dwhere the sea ground is located.- vThe network 5 is designed to simulateclosely the electrical characteristics of the conductors 1 and 2, andthe network 7 to simulate the characteristics of the submarine cableextending vfrom the point B to its distant end. The terminal circuit S2is similar to the circuit S1 comprising the ratio arms '15 and 16 whichhave their midpoint connected with the. sea ground and having bridgedacross Brid ed across the ratio arms is a 1 them the winding 17 of thetransformer T1.

The secondary winding 18 of the trans' amplifier A1. The output side ofthe said amplifier is adjustably connected across the impedance Z2 ofthe input circuit of the receiving apparatus R1. The ratio arm 15 isconnected with the conductor 3 extending from the point' A of theterminal circuitto the point B and is there connected with the network 9which simulates the characteristics of `the Submarine cable which isconnected with the conductor 1 at the point B. The other ratio arm` 16.is connected with an artificial line comprising the networks 6 and 8which, in turn, are connected with the conductor 4 which extends fromthe point C to the point D at the sea ground. The net-work 6 is designedto simulate electrically the characteristics of the conductors 3 and 4and the network 8 is designed to simulate and to balance the network 9which is located at the sea ground.

Fig. 2 shows schematically a preferable form of arrangement for cablingthe conductors that extend from the terminal circuit to the sea ground.Since the conductors 3 and 4 have to transmit onlyl the current inducedtherein by the source of inter# ference, they may be of much smallergauge of wire than conductors 1 and 2 which are designed to transmit notonly interference currents but also the signaling currents.

The arrangement shown in Fig. 3 differsfrom that shownin Fig. 1 in thata single common conductor 5 extends from the joint terminal circuits S3and S4 to the sea ground at the point D.' In this figure, the partscorresponding to similar parts in Fig. 1 have been given the samedesignations. The transmitting device 12 connected to the midpoint oftheratio arms of the circuit S3 and the conductor 2O connected with themidpoint of the circuit S,1 are connected over conductors 21 and 22 withthe conductor 5 extending to the sea ground. The arrangement of thebalancing networks of the artificial lines in Fig. 3 differs from thatshown in Fig. -1 in view of the fact that in Fig. 3 the cable extendingfrom the terminal circuit to the sea ground comprises only threeconductors instead of four as shown in Fig. 1. In the artificial line asshown, the network 7 simulates electrically the characteristics of thesubmarine cable extending from the point B to its distant end. Thenetworks 5 and 6 simulate the characteristics of the conductors 1, 3 and5 and the network 8 balances the network 9 which is connected with theconductor 3 at the seav ground and which is designed to simulate thecharacteristics of the sub-1 marine cable connected with conductor' 1.

The distant end of the cable shown in Fig. 3 has connected therewith aterminal circuit which maybe either of the types shown in Figs. 1 and 3or of any other well-known type for terminating telegraph cables.

Having in mind'the foregoing description of the various parts of thecircuits andthe function that each is to perform the invention will beclearly understood from the following description of the manner in whichthe result is attained.

Considering first the arrangement shown in Fig. l, if a source ofinterference impresses itself upon conductors 1 and 2 the current set upin conductor l will be somewhat different from that set up in conductor2 due to the fact that the impedance to ground of the conductor 2 at thepoint D is different from the impedance to ground of the conductor 1 atthe point B, and even though the points B and D coincide there willstill be sufficient unbalance as to cause -an interfering difference ofpotential to impress itself across the arms 10 and 11 of the terminalcircuit S1. Such difference of potential will, of course, ymanifestitself in the receiving apparatus R1. In view of the close physical/relationship of the conductors 3 and 4 with 1 and 2 the interferencethat sets up the difference in potential in conductors 1 and 2 willsimilarly affect 3 and 4. Since conductor 3 together with the lbalancingnetwork'9 at the sea ground closely simulates conductor 1 and thesubmarine cable connected therewith, and likewise conductor 4 simulates2, the unbalance between 3 and 4 will be (substantially the same as thatbetween 1 and 2,. This unbalanced voltage will impress itself across thearms 15 and 16 and will be induced in the winding 18 of the transformerT1. The drop in potential across the impedance Z1 will be impressedacross the input side of the amplifier A1 andthe resulting current willbelimpressed across the impedance Z2. By arranging the circuits so thattheV interference voltage set up in conductors' 3 and 4 is opposed tothat set. up in 1 and 2 and by adjusting the values of Z1 and Z2 and thedegree -of amplification of A1 .substantial elimination-ofinterferencewill be effected.

If the conductors 2 and 4 are grounded at the same point as conductor 3the neutralization will be effected in the manner just described. If,however, the conductors 2 and 4 are both grounded at'the same pointwhich is closer to'the receiving terminal than the grounding point ofconductor 3 the terminal circuit S2 will be required to neutralize moreof the disturbance im' n interference voltage impressed upon theconductor 1 between the terminal circuit and the point B.

v In the` arrangement shown in Fig. 3, the conductor 5 is common to thecircuit of conductor 1 and also of conductor 3. If a source ofinterference acts upon the cable contain- Aing conductors 1, 3 and 5 adifference of potential will be established between conductors 1 and 5and likewise rbetween conductors 3 and 5. The difference of' potentialbetween 1 and 5 will be impressed across the ratio arms and 11 of theterminal circuit S3 and eventually will be impresesed upon the receivingcircut'comprising the Winding 14 and the impedance Z2. Similarly, thedifference of potential between conductors 3 and 5 will be impressedacross the ratio arms and 16 of the terminal circuit S, which results'inestablishing a di'erence in potential across the impedance Z1.This-dider-V ence of potential may be passed through a vacuumV tubedevice either with or without titl dit

amplification and be impressed across the impedance Z2 of the inputcircuit of the receiving apparatus R1. By properly adjusting Z1, Z2 andthe amplification of A, neutralization may be effected.

it will be seen that the arrangement discloses means for neutralizinginterference in submarine telegraph cables which by means of anartificial network located at the sega groundavoids the necessity ofextending the shielding conductor for a great distance along the lengthof the submarine cable to be protected. This arrangement, furthermore,discloses means whereby a single conductor may be'substituted for twoconductors constituting the other side of the cable circuit `and of theshielding circuitrespectiv'ely.

Although this invention has been shown as embodied in certain specificforms, it is manifest that it is capable of embodiment -in other anddi'erent `forms without departing from the spirit and'scope of theappended claims. p

1. ln lan electrical interference neutralizing device, the combinationof a transmission circuit comprising a grounded signalingV conductor anda grounded return conductor, a second circuit one side of whichsimulatesby natural'and artificial means the grounded-signalin conductorof said transmission circuit an the other side being the grounded returnconductor common to.

said first circuit, both of the said circuits -being exposed tosubstantially the same interference,- balanced terminal circuits foreach of the said circuits, and means associa-ted with `thel saidterminal circuits for opposing the interference. voltages set up in 2.In an electrical interference neutralizing device, the combination of atransmission circuit comprising a grounded signaling conductor and a.grounded return conductor, a second circuit one side of which simulatesby natural and artificial means the grounded signaling conductor of saidtransmission circuit and the other side Vbeing the rounded returnconductor common to said rst circuit, both of the saidcircuits beingexposed to substantially the same interference, balanced terminalcircuits ir'or each of said circuits, and means associated with the saidterminal circuits comprising a unilateral device whereby theinterference volt- `age set up in said second circuit may be impressedupon the receiving circuit of the. said transmission circuit inopposition to the interference voltage impressed directly upon saidreceiving circuit from said transmission circuit, the` said unilateraldevice preventing reaction of the said transmission circuit upon thesaid second circuit.

3. ln an electrical interfere-nce neutralizing device, the combination'of a submarine cable signaling circuit adapted `t'or duplex operation, asecondcircuit having one conductor in common with said first circuit,and a second conductor extending through the zone of interference withthe said signaling circuit and having an artificial network inserted atthe sea ground in order that the said conductor may have the saineiinped` ance to ground as the signaling conductor of the signalingcircuit,- and means to impress the interference voltages set up in eachof said circuits upon a common circuit in such manner as to neutralizeeach other.

4. lin a system for neutralizing interfermission system by a sourceexternal to the.

transmission system itself, the combination with a submarine cable of aterminal circuit having ratio arms and a receiving circuit connectedacross the' extremities of the said arms, a second terminal circuit alsohaving ratio arms and a receiving circuit connected across theirextremities, an artificial cablesimulating said submarine cable, aconnecting cable having three conductors of which the first connects thesubmarine cable to one ratio arm of its terminal circuit, the secondconnects one ratio arm of the second terminal circuit with an artificialcable located at the sea-ground of the system, the third conductorhaving one end connected with the sea-ground, a sec` 'ond artificialline having one side connected with the said third conductor and havingits other side connected with the other ratio arm of each terminalcircuit, and means for connecting the receiving circuits y. of bothterminal circuits to neutralize interfering currents set up in saidreceiving circuits by voltages created inthe said connecting calll@ lil)

ist

ble by sources extraneous to the system itself.

5. In a system for neutralizing interfering currents set up in asignaling transmission system by a source external to the transmissionsystem itself, the combination with ,a signaling Wheatstone bridgenetwork comprising two ratio arms, a third arm including one conductorof a terminating cable, a submarine cable having a grounded receivingdevice at the distant end thereof and a second conductor of aterminating cable connected with a seaground, and a fourth arm balancingthe said third arm comprising artificial lines simulating each oftheelements of the said third line, a non-signaling `Wheatstone bridgenetwork comprising two ratio arms, a third arm including a thirdconductor of the said terminating cable, an artificial line grounded atthe sea-ground and balancing the said submarine cable, the said thirdarm also including the said -second conductor of the said terminatingcable which is common to the third arm of both networks, and a fourtharm comprising artificial lines balancing the said ythird arm, areceiving circuit for each VVheatstone bridge network connected acrossthe ratio arms thereof, and means connecting the said receiving circuitshaving therein a unilateral device controlling the magnitude of theinterfering current impressed upon 'one receiving circuit by the otherand preventing reaction between the said circuits.

6. In a system for neutralizing interfering currents set up in asignaling transmission system by a source external to the transmissionsystem itself, the combination withJ a signaling cable `of themulticonductor terminating cable exposed to an external source ofinterfering voltage, they first of the said conductors being connectedwith the said signaling cable, the second conductor beingconnected to asea-ground and the third` conductor being connected at the sea-groundwith an artificial line simulating the saidl signaling, cable, two

ratio arms of a Wheatstone bridge circuit, one of which is connectedwith the first conductor of the terminating cable, another group of tworatio arms of a second W'heatstone bridge circuit,l one of which isconnected with the second conductor of thev terminating cable, an arti--ficial line constituting the third arm of each VVheatstone bridgecircuit connected with the remaining arm to each group of ratio arms,and also connected with the said third conductor of the terminatingcable to balance the fourth arm of each bridge, a receiving circuitconnected with each group of ratio arms, and means to equalize andoppose the interfering currents set up in each receiving circuitresultin from a voltage set up in the conductors o the terminating cableby the said external source of ini erference;

7. In a system for neutralizing interfering currents set up in asignaling transmission system by a source external to the transmissionsystem itself, the combination with a Wheatstone bridge signalingcircuit having two ratio arms, a third arm comprising the signaltransmission circuit and the fourth arm comprising an artificial line tobalance the said third arm, of asecond lVheatstone bridge circuit havingtwo ratio arms, a third arm comprisinor a real line and an artificialline, a part of the said real line being common to the third arms ofboth bridge circuits, and a fourth arm comprising an artificial line tobalance the said third arm, a receiving circuit individual to andconnected to each bridge circuit, and means connecting both receivingcircuits and rhaving therein a unilateral device for controlling themagnitude of a current transmitted therethrough and for preventingundesirable reactions between the receiving circuits. l

In testimony whereof, I have signed my name to this specification this13th day of August 1920.

oT'ro B. BLACKWELL.

